Vaisala HM34 - Manual (Page 5)

3. CALIBRATION AND MAINTENANCE
Calibration and maintenance of the meter should be performed
at regular intervals which depend on the conditions of use and
the desired accuracy, but at least once a year. A one point
calibration may be performed for the HM34 meter by adjusting
the trimmer potentiometer marked "DRY" (Fig. 2). This field
calibration can be performed against a calibrated Vaisala humid-
ity meter. For a higher-accuracy two-point calibration use a
Vaisala HMK11 calibrator and saturated salt solutions as de-
scribed in the Operating Manual of the HMK11. The calibration
is done first for the dry end and then for the wet end by adjusting
trimmer potentiometers "DRY" and "WET" respectively. The
potentiometers are located under the protective lid of the battery
compartment (Fig. 2).
Replacing the sensors
When you replace a defective H-sensor package with a new one,
make sure you handle the package with care. After installation,
calibrate the humidity sensor. If the "WET" trimmer potentiometer
has not been adjusted from its factory setting, a one point
calibration is sufficient. Otherwise, perform a two point calibra-
tion with an HMK11 calibrator. Replacement of the Pt 100
temperature sensor requires no recalibration.
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